1. Field of the Invention
The present invention relates to a technique for providing compatibility between high-definition color television (HDTV) and present day conventional color television. More particularly, the present invention relates to a technique which provides a television signal which is capable of being converted by simple and inexpensive means into either a high-definition TV picture signal for use by a HDTV receiver or a conventional standard picture signal for use in present day receivers such as, for example, a National Television System Committee (NTSC), Phase Alternation Line (PAL) or SECAM system signal.
2. Description of the Prior Art
Present day conventional television using, for example, NTSC or PAL system signals provide fairly good color pictures if the receiving conditions are good. Such pictures, however, do not come close to having the sharpness, realism and visual impact as might be found, for example, in a motion picture film or a magazine quality picture. To provide dramatically better television picture quality, experimental studies have been performed and components have been developed in an attempt to provide High-Definition Television (HDTV) pictures which approach the quality of a 35 mm color film. Such high resolution TV has been deemed especially advantageous for use, for example, in wide screen theater and home TV projection and for theatrical motion picture production and projection using magnetic tape instead of film.
Several HDTV systems have already been proposed, the parameters of which are generally disclosed in the article "The Future of High-Definition Television: First Portion of a Report of the SMPTE Study Group on High-Definition Television" by D. G. Fink in SMPTE Journal, Vol. 89, No. 2, February 1980 at pp. 89-94 and its conclusion in Vol. 89, No. 3, March 1980 at pp. 153-161. In the systems disclosed therein, the lines per frame range from 1023 to 2125, the aspect ratios (picture width to picture height) range from 4:3 to 8:3 and luminance bandwidths range from 20 to 50 MHz. The recommendation of this group was that a HDTV signal should be capable of a standards conversion that would provide service to NTSC, PAL and SECAM domestic services. After three years of study, however, this group concluded that a HDTV system compatible with the existing domestic services is not feasible by any means known to or envisaged by the Study Group, in view of HDTV aspect ratios and bandwidths. They furter concluded that adoption of a non-compatible HDTV system for home use in problematical and would occur only after prolonged exposure to the public of HDTV projected images in theaters.
A description of one of the systems considered by the SMPTE Study Group is found in the articles "High-Definition Television System-Signal Standard and Transmission" by T. Fujio et al in SMPTE Journal, Vol. 89, No. 8, August 1980 at pp. 579-584 and "Research and Development on High-Definition Television in Japan" by K. Hayashi in SMPTE Journal, Vol. 90, No. 3, March 1981 at pp. 178-186. These articles discuss the 1125 scan line, 5:3 aspect ratio, 20 MHz luminance bandwidth system being developed in Japan. Compatibility with conventional receivers is not discussed or considered.
Other techniques labeled as either high-definition or high-resolution television systems have modified the transmission of the conventional TV signal to, for example, provide increased horizontal line resolution or better luminance resolution with less objectionable subcarrier pattern. In this regard see, for example, U.S. Pat. No. 2,686,831 issued to R. B. Dome on Aug. 17, 1954 where large area flicker is allegedly canceled by subdividing the TV picture signal into three contiguous bands and transmitting each of the three bands in a certain manner during the normal sequence of a conventional picture signal. See also U.S. Pat. No. 4,296,431 issued to K. F. Holland on Oct. 20, 1981, wherein the picture signal has one of the color axes inverted at a first rate while the second color axis is inverted at a second, different, rate to provide better luminance resolution and better subcarrier pattern than allegedly found with the normal conventional signal.
Another technique for improving the horizontal and vertical definition and reducing low frequency flicker in a conventional picture is disclosed in the article "Concepts For A Compatible HIFI-Television System" by B. Wendland in NTG-Fachber (Germany), Vol. 74, September, 1980, at pp. 407-416. There is disclosed an arrangement wherein the picture quality can allegedly be improved using digital signal processing technologies. Offset sampling is used to improve horizontal definition, and a double rate stored image readout at the receiver selects the appropriate signal portions to subjectively increase the vertical definition and reduce low frequency (25 Hz) flicker. The latter three references, however, are only attempts to improve conventional television receiver picture quality and do not provide resolution comparable to a 35 mm film or magazine quality picture.
An important aspect of introducing any new service is its degree of compatibility with existing serrvices. For example, color TV was implemented having full compatibility with the then existing monochrome TV standard. Therefore, the problem remaining in the prior art is to provide methods and apparatus for transmitting a television picture signal which can be made compatible for use by either a NTSC, PAL or SECAM system receiver to produce a conventional TV picture or a high-definition television receiver to produce a picture approaching that of a 35 mm film.